1. Field of the Invention
This invention relates to cellular polyurethanes and is more particularly concerned with flame retardant flexible polyurethane foams and with processes for their preparation.
2. Description of the Prior Art
Fire retardant flexible and semi-flexible polyurethane foams which are characterized by good physical properties and good fire resistance are well known in the art; see U.S. Pat. No. 3,909,464 and the art cited therein. The patent discloses the very efficacious combination of antimony oxide, a polyhalogenated aromatic compound and alumina trihydrate. The latter is not actually a hydrate but is rather a true hydroxide.
The use of inorganic hydrated salts as fire retarding agents has been recognized in the polymer art in general and in polyurethanes in particular; see Japanese specification No. J5 4149796, which, typically, discloses the use of salts such as calcium chloride hexahydrate in polyurethane foams.
However, the prior art also discloses the use of the same kinds of inorganic hydrated salts as blowing agents for polyurethanes through the action of the hydrated water with the isocyanate to produce carbon dioxide. In fact, the use of such materials as fire retardants in foams has been greatly hampered by their tendency to produce very low density foams because of unwanted blowing action. Typically, the use of calcium chloride hexahydrate, magnesium sulfate heptahydrate, sodium sulfate decahydrate, and the like as blowing agents in cellular polyurethanes is disclosed in Polyurethanes Chemistry and Technology, Part II, Saunders and Frisch, page 285, 1964, John Wiley and Sons, Inc., New York, N. Y.; Plastic Foams, Part I, Frisch and Saunders, page 139, 1972, Marcel Dekker Inc., New York, N. Y.; and U.S. Pat. No. 2,981,700.
Surprisingly, it has now been discovered that certain true hydrated inorganic salts can be employed in place of the alumina trihydrate in the fire retardant combination disclosed in U.S. Pat. No. 3,909,464 cited supra, without there being a problem with excessive or unwanted blowing action in the formation of fire retardant polyurethane foams. In fact, the flexible foams in accordance with the present invention have physical properties equal, and, in some cases superior, to those of the cited art.
Further, and even more unexpected, the fire resistance of foams in accordance with the present invention is superior to that of the foams according to U.S. Pat. No. 3,909,464 cited supra.